Horizontal surfaces

Section 7 7 A Fischer projection shows how a molecule would look if its bonds were projected onto a flat surface Horizontal lines represent bonds coming toward you vertical bonds point away from you The projection is nor mally drawn so that the carbon chain is vertical with the lowest num bered carbon at the top... 

Figure 46-6. Flow of membrane proteins from the endoplasmic reticulum (ER) to the cell surface. Horizontal arrows denote steps that have been proposed to be signal independent and thus represent bulkflow. The open vertical arrows in the boxes denote retention of proteins that are resident in the membranes of the organelle indicated. The open vertical arrows outside the boxes indicate signal-mediated transport to lysosomes and secretory storage granules. (Reproduced, with permission, from Pfeffer SR, Rothman JE Biosynthetic protein transport and sorting by the endoplasmic reticulum and Golgi. Annu Rev Biochem 1987 56 829.)...

Heat transfer coefficient a (for free convection) for heating from a wall a = 3-6 W/m2 K (surface vertical), for floor heating a = 6-10 W/m2 K (surface horizontal) and no heating from ceilings, as the temperature gradient would suppress convection ... 

Consider a molecule X Y Z, where X is the substituent, Y the constant part of the molecule (the link between X and Z), and Z the reaction center. Now we wish to compare its reactivity with the molecule H Y Z bearing hydrogen as the reference substituent. The electronic influence of the substituent X may depend on whether it comes into contact with the surface or not. In terms of adsorption this means whether the molecule will be attached to the surface horizontally or perpendicularly ... 

According to the vendor, the geologic formation is a limiting factor in the depth at which horizontal drilhng is performed. Formations with vertical fractures that can extend to the surface can pose limitations because driUing fluid can breakout at the surface. Horizontal drilling only improves access to the contaminants and must be combined with a remediation technology. 

Fig. 8.6. Potential curves of Vvs. h in the transitive state model (a) and the collision model (b), where EA and Ed are the adsorption and desorption activation energies, respectively Q is the heat of adsorption, h the distance from the surface (horizontal axis of the figure).

In recent years attempts have been made to improve the gas-liquid mass transfer by changing the design of the mechanically agitated vessel. Mann et al. (1989) evaluated the use of horizontal baffles mounted near the gas-liquid surface. Horizontal baffles prevent vortex formation, generate less shear than standard baffles, increase gas holdup, and improve gas-liquid mass transfer. The latter two results are due to the rotational flow below the baffles, which causes gas bubbles to move upward in a spiral trajectory and induces surface aeration. For a 12-inch i.d. and 18-inch-tall stirred vessel, they showed kLat to be improved by a factor of 1.6 to 2.3 with 30 to 50% lower agitation power compared to the standard vessel. 

In practice, it is found convenient to express the pressure loss for all types of fully developed internal flosvs (laminar or turbulent flows, circular or noncLrcu-lar pipes, smooth or rough surfaces, horizontal or inclined pipes) as (Fig. 8-19)... 

Rotate unit through 90° perpendicular to the plane of the monolayer so that it now lies flat on its base with the culture surfaces horizontal. 

Instrumentation. In a typical CLSM experiment, a narrow laser beam scans a surface horizontally, i.e. at constant height, in x- and y-directions using piezo-driven mirrors. A small pinhole is located in front of an optical detector at a position conjugate to the focal point in the sample plane. This way, the detector measures the intensity of light reflected from the surface at every scanned position. Light scattered from out-of-focus positions is focused outside the pinhole and thus does not reach the detector. An image of scattered and/or reflected laser light intensity is created... 

Fig. 37. Bom-Haber energy cycle depicting CO desorption from R and Au surface atoms (vertical arrows) and core level photoemission from a clean and CO covered Pt(l 11) surface (horizontal arrows) [83Ege, 86Duc].

Fig. 44. Real part of the optical reflectance anisotropy spectra for clean Cu(llO), oxygen covered (2xl)-O-Cu(110) and CO covered (2xl)-CO-Cu(l 10) surface. Horizontal lines indicate zeros of each spectrum [95Hof]...

Thermal and electric contact resistances are taken into account as a function of local temperature and are referred to a specific contact surface (horizontal and vertical) between the different elements of equipment, i.e., die/compact, punch/ compact, punch/die, and graphite-spacer/punch, as shown in Fig. 6.7 [31]. As a result, the obtained contact conductances and thermal conductivities are in the range of 5 X 10 -7 X 10 S m and 3 x 10 -2 x 10 W m K respectively. 

Scraped surface horizontal film (votator) Especially for viscous feed. OK for foaming, for fouling, crystal formation and suspended solids. Viscosities > 2000 mPa s. Relative to agitated film retention time of 1 1 and volume 1 1. Overall heat transfer coefficient 2 kW/m °C decreasing with increasing viscosity. Power 3 to 12 kW/m. Related to scraped surface reactor. Section 6.20. 

Each employee on a walking/working surface (horizontal and vertical surface) with an unprotected side or edge which is 6 feet or more above a lower level shall be protected from falling by the use of guardrail systems, safety net systems, or personal fall arrest systems. 

Equipment with tubeside condensation are more easily vented, provided condensate is not permitted to flood the heat transfer surface. Horizontal units may experience maldistribution or higher rates of condensing at the top of the unit than at the bottom of the unit. Multipass tube arrangements help to avoid this problem. Condensate loading in the tubes must not be so high as to prevent proper venting. This is discussed in Chapter 22. 

In-bed surfaces Horizontal or vertical tubes may be inserted as heat transfer surfaces... 

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